Hidezumi Kato

Compressive deformation of Y2O3-stabilized ZrO2/Al2O3 composite

Compressive deformation of 80wt% ZrO2 (3mol% Y2O3)/20wt% Al2O3 composite was studied in air at temperatures from 1400° to 1550°C Extraordinary large deformation (up to -1.8) was observed at strain rates from 10-3 to 10-4s-1. The stress exponent was from 1.2 to 2 and activation energy was 620±40kJ/mol. It was observed that the Al2O3 aggregate evolved during the deformation. This phenomenon was explained by the grain rearrangement model as a consequence of grain switching doring the superplastic flow.

Superplasticity of mullite-zirconia composite

Tension tests of mullite-zirconia composite were conducted at elevated temperature. A superplastic elongation of 122% could be achieved at an initial strain rate of 2.86×10−5s−1 at 1550°C. Strain hardening was observed at strain rates from 1.42×10−4 to 2.86×10s−5s−1 at 1550°C. The addition of zirconia grains to the mullite matrix increased the creep rate of the composite.

Diffusion bonding of ceramics: mullite, ZrO2-toughened mullite

Diffusion bonding of fine-grained mullite and ZrO2-toughened mullite was performed in the temperature range from 1500 to 1550 °C in air. Uniaxial pressure was applied at high temperature during the bonding process. The surface roughness to be bonded (Rmax) was about 3 μm. Bonding strength was measured by four-point bending tests and the strength of the base material was measured by three-point bending tests. The effects on the bonding strength of bonding conditions such as temperature and applied strain were examined. Bonding strength increased with increasing bonding temperature and applied strain. The bonding strength of mullite and ZrO2-toughened mullite was about 80% of the strength of the base material before bonding. The bonding strength of mullite was maintained up to 1000 °C.

Compressive deformation properties and microstructures in the superplastic Y-TZP

The superplastic deformation properties of 3mol% Y2O3-stabilized tetragonal ZrO2 polycrystals (Y-TZP) were studied by uniaxial compression tests in air at temperatures up to 1500°C with strain rates ranging from 10-3 to 10-5s-1. The effect of microstructure on the superplasticity was also examined, Fine-grained Y-TZP with an average grain size of 0.3-0.4μm was deformed to the true strain of more than -1.5. The macroscopic strain rate (e) in superplasticity was expressed phenomenologically by the following equation, e=2×10-5exp(-380000/RT)σ2.1/d1.8, where T, σ, and d are temperature, stress, and grain size, respectively, and R is the gas constant. Although the microstructure of the deformed specimen showed slight grain growth and slight anisotropic deformation of each grain, the large strain was mainly caused by the grain boundary sliding. The cavitation was not observed in the compressed specimens. ZrO2 particles maintained tetragonal or cubic phase after the superplastic deformation. The deformation properties and the observed microstructure in the superplasticity of Y-TZP were explained by the Gifkinss model.